of east orange



. I l l I l r l I II Dec. 31, 1929.

r INVENTOR TA-ltruLM -5 EM BY v ATTORNEY Patented D... 31, 1929 I i,741,zz6

UNITED STATES; PATENT OFFICE SoN, INCORPORATED, OF WEST ORANG JERSEY Application filed April 18,

' This invention relates to an electromechanical translating: device and more particularly to such a translating device adapted to operate at sound frequencies, and is particularly applicable to phonograph pick-ups, lound speakers, microphones and the like.

It is an object of this invention to provide a device of the class described,'which shall be simple, rugged and economical in construc- 10 tion, reliable operation, and compact, without, however, requiring extremely precise workmanship in construction.

It is a further object of this invention to provide a device of the class described, in

which the customaryarmature of magnetic material and its accompanying fine wire coil is eliminated.

It is still a further object of this invention to provide a device of the class described, in

which the distortions, due to saturation of an armature of magnetic material, are eliminated.

The features of novelty which I believe to be characteristic of my invention are set forth with. particularity in the appended claims.

My invention itself, however, both as to its fundamental principles and as to its particular application will best be understood by reference to the specification and accompanyin drawing, in which:

figure 1 is a view in'side elevation of a phonograph pick-up according to my invention, and showing, diagrammatically, an amplifier and loud speakerassociated with the pick-up. i

' Figure 2 is a front elevation view of the phonograph pick-up of Figure 1.

Figure 3 is a detail sectional view on an enlarged scale, taken on lines 33 of Figure 1. 40 Figure 4 is a diagrammatic view showing the operation of my invention, and also showing' he invention adapted for use as a microphone or. lound-speaker. I

In apparatus of the class described, as gen erally constructed, there is provided 'a magnet, a winding for the electric currents to be utilized orgenerated, and an armature of magnetic material, usually of iron, arrang d foivvibration in the field of the magnet in such manner as to provide a change of flux of the mechanical vibrations.

THEODORE m. EDISON, 0E EAST ORANGE, NEW JEEsEY, ASSIGNOR 'ro THOMAS A. EDI- E, NEW JERSEY, AcoEroEA'rIoN OF NEW ELECTROMECHANICAL TRANSLATING DEITICE 1928. Serial No. 270,861.

with respect to the conductors of the 'coil. The coil is customarily in the form of a winding embodying a large number of turns of finewire, the resistance and impedance of which are relatively high. 5 In the operation of such a device a certain amount of distortion is introduced by hysteresis losses in the armature. Furthermore the law of operation of such a device'shows that there is a tendency to setup additional 0 electrical variations of double the frequency Moreover, since the wire used in the coil is-very fine, there is great danger of open circuits or short circuits in the windings.

In accordance with .my invention, I eliminate these difficulties by providing a nonmagnetic conductor including a loop having a portion mounted for movement in a magn'et'c field of fixed value, such portion of the con uctor being arranged to move through a field which is substantially constant within the limits of movement, whereby the output of the device is very free from distortion. I The said portion of the conductor is prefer ably in the form of a U disposed in the air gap substantially parallel to the pole faces of the magnet. The upper open ends of the U are flexibly mounted in such a manner as to permit them to move toward and away so from each other when the base of the U is moved in a direction approximately parallel to the arms of the U. Such movement, as will be understood, causes a change in the number of lines of magnetic flux enclosed by the U, s5 and the loop of which it is a part, and thereby causes the generation of.an electro-motive force which is linearly proportional to the rate of change of flux enclosed by the moving portion of the conductor, as long as the flux density of the field in which the said portion of the conductor moves is constant.

Referring 'now more particularly to Figure 1, in which I have shown my invention as applied to a phonograph pick-up, 1 desi nates the energizing magnet having po e pieces 2 and 3 defining an air gap, within which the movable portion of the non-magnet'zc conductor acted upon by the magnetic flux is vibrated. The said movable portion of 1 the conductor is preferably in the form of a single relatively heavywire or ribbon bent in the form of a U and having arms 4 and 5.

v The upper ends of the arms a and 5 are carried on terminal contacts 6 and 7 respectively,

which are clamped between an internal support 10 mounted within the magnet 1, and

cover pieces 8 and 9, and held firmly in position by means of s'crews ll and 12 engaging the support block 10. The .downwardly extending portions of the terminals 6 and 7 are preferably tapered and bent inwardly as shown at 6 and 7 to increase their flexibility and engage the upper ends of the arms 4 and 5 of the U, where a suitable low resistance connection is established, as for example, by soldering. The upper ends of the terminals 6 and 7 are preferably bent outwardly and twisted as at 6 and 7 to provide for connections with suitable leads. The lower end of the U is secured to one end of astylus bar or link 13 carrying at its opposite end a suitable stylus point 15 adapted to engage a record 16, to be vibrated thereby as the as record is revolved-by the turntable 17. The

. between the arms 18 and 18 of a support'21,

which in turn is inserted in a hollow tube 25, and the support 21 may be secured in position in the tube in any suitable manner, as for example by means of pin 22 passing through the tube 25 and the support 21.

'The tube 25 is pivotally mounted at its opposite end on a forked member 26, which,

in turn, is rotatably mounted in a suitablesupporting sleeve "27, to provide for movement of the pick-up in following the record groove. 7 1

In the case of avertical cut record for which the pick-up .shown is primarily adapted, suitable feed mechanism may' be provided for advancing the pickup as the turntable is rotated. Since such mechanism forms per so no part of the'present invention, and since any known mechanism may be used for the urpose, it is not shown.

The eads 28 and 29 which are connected 7 to the terminals 6" and 7" may be passed into the tubular support 25 throughsuitable openings therein and carried out to the desired point. Any suitable arrangement of amplifier may be used, if desired; after ampli fication, the currents may be paa ed into a suitable loud speaker 41. Since the resistance and impedance of the pick-up itself are very low, a very high step-up transformer should be interposed between the pick-up and the amplifier, in case the usual form of thermionic vacuum tube amplifier is utilized. In the arrangementshowmthe leads '28 and 29 may be connected tothe primary winding 30 of a suitable transformer comprising a core 31 of magnetic material and a secondary winding 32, which is connected to the input circuit of the amplifier 40. To obtain the best results, the resistance'and impedance of the primary winding 30 should be kept relatively low in order to match that of the pickup, while the characteristics of the secondary winding 32 should be made to match those, of the amplifier 4:0.

I have obtained very satisfactory results with the construction shown when the primary winding 30 consists of only a few turns of heavy copper ribbon, while the secondary winding 32 is in the form customary for audio frequency windings operating in the input circuit of the usual vacuum tube amplifier.

Referring now more particularly to Figure 4, I have shown diagrammatically the method of operation of the [movable portion of'the conductor disposed in the magnetic field according to my invention. In this figure, the normal or static position of the said movable portion or -U of the conductor is shown in the full lines while the dotted'lines show the position of the same after movement away from the normal position. Assuining that the stylus point 15 is movedin an upward direction by the rotation of the record 16, the opposite end of the lever 13 will be moved downwardly, thereby tending to move the lower end of the U down: this, In turn, will pull the lower ends of the wings 6* and 7 down and cause them to bend outwardly, as shown in dotted lines in Figure 4, in which the movement taking place is exaggerated for the purpose of illustration.

Th s, in turn, causes an outward bending or deformation of the upper ends of the arms 4 and 5, thereby oh the cross sectional area of the magnetic flu'x enclosed by the U and bythe. loop of --which the U is a part. Since the 4 and 5 move in opposite directions, and are connected in series by the connection at the bottom of the U, the voltage generated in the said arms will be in phase and will .add to produce a voltage equal to twice that generated'in each arm.

It is tobe noted particularly, that by making the pole pieces 2 and 3 sufliciently wide so that the magnetic field density within the.

limits of movement-of the moving U is essentially constant, the voltage generated will be very closely proportional to the movement of the arms of the U transversely thefield, as a result of which the voltage generatedis particularly freefrom distortion of the type which occurs with the usual form f vibrating armature, in which the relucspeed-of 2 I position of the armature.

It will be understood that the principles of my invention may be applied in other forms of apparatus, such for example as loud speakers and microphones. For example, in Figure 4, I have shown a suitable diaphragm 38, such as a cone, secured to one end of adriving rod 35, as for example by means of nuts 36, the other end of the driving rod being secured to a link or member 13 which is rigidly connected to the closed end of the U disposed between the pole pieces of the magnet 1. In the operation of my device asa loud speaker, the telephone currents for actuating the speaker are supplied to the terminals 6 and 7, and thence to the movable U, the movement of which is substantially the same regardless of whether the apparatus is employed as a motor or as a generator. The apparatus shown in Figure 4 may thus be utilized either as a loud speaker or as a microphone. In case it is desired to operate the" apparatus as a microphone, the sounds to be picked up are allowed to impinge against the diaphragm 38, thereby producing movement of the movable U, and in turn causing the generation of currents corresponding to the sounds to be picked up. 7

While I have shown a phonograph pickup particularly adapted for operation with vertical cut records, it will be understood that such a pick-up. may be readily adapted to lateral cut records, by mounting the stylus arm so that the stylus point 15 vibrates laterally instead of vertically, and by mountingthe pick-up in a horizontal position.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modifications and changes may be made without departing from vice comprising in combination a mavnet having an air gap, a non-magnetic conductor including a portion in theform of a U mounted in said air ap and having the open ends of said U yiel ably supported for movement at an angle to the arms of said U, and a vibratile member secured to the closed end of said Us 2. A phonograph pick-up comprising in combination a mag'net'having an air gap, a non-magnetic conductor in the form of a U ended loop portion disposed in said air gap,

means for yieldably supporting the open ends of said loop portion for movement at an angle to the sides or arms of such loop portion, a stylus arranged tobe vibrated by a record, and a connection between said stylus and the closed end of said loop portion.

This specification signed this 17th day of April 1928.

- THEODORE M. EDISON.

mounted in said air gap, means for yieldinga l y supporting the open ends of said conductor for movement at an angle to the arms of said U, a stylus arranged to be vibrated b a record, and a connection between sai stylus and the closed end of said conductor.

3; An electro-mechanical translating device comprising in combination a magnet having an air gap, a non-magnetic conductor including an open-ended loop portion disposed 

